We both have enjoyed a lot surfing in north Sardinia with our Evo.
I'm in love with mine: it help me in all conditions !!

We have noted that even if we leave our boards under the sun, when we unscrew the valve no "hot air" seems to come out from the hole(no "psss" can be heared while unscrewing the valve).
We have other boards with valve and far all we hear the classic "pssss" when we unscrew the valve after sun exposure.

Good to hear you like your boards. Regarding "psssss", it depends also on what the temperature was when you closed your valves and also sometimes on how you unscrew them. Sometimes the valve open kind of smoothly and you will not hear a pssss.

You could try first ope and close the valve when the board is a bit cold, then heat it up a bit (nothing too drastic though) and try the unscrewing the valve again.

If your worried, try to get some local expert to have a look at the boards for cracks etc, but it is HIGHLY unlikely both boards would have some kind of subtle defect.